Crystallization and preliminary X-ray diffraction studies of the WW4 domain of the Nedd4-2 ubiquitin-protein ligase

Ubiquitin-mediated protein modification via covalent attachment of ubiquitin has emerged as one of the most common regulatory processes in all eukaryotes. Nedd4-2, closely related to neuronal precursor cell-expressed developmentally down-regulated 4 (Nedd4), is a multimodular ubiquitin-protein ligase comprised of four WW domains and a Hect domain. The WW domains recognize the proline-rich motifs on the multi-subunit amiloride-sensitive epithelial sodium channel (ENaC). To gain insights into the binding of the WW domain to proline-rich peptides, a protein fragment (78 amino acids) containing the fourth WW domain (WW4) of the Nedd4-2 protein was purified and crystallized and X-ray diffraction data were collected. A data set was obtained to 2.5 Å resolution from a cryocooled single crystal at a synchrotron source. The crystals belong to the tetragonal space group P4₁2₁2 (or P4₃2₁2), with unit-cell parameters a = b = 113.43, c = 103.21 Å. Analysis of the self-rotation function suggests the presence of four WW4 molecules in the asymmetric unit, with a high unit-cell solvent content of 74%.